A. Field of the Invention
The present invention relates to a system and method for removing and replacing vehicular hydraulic fluid. In particular the present invention relates to an apparatus for removing and replacing the hydraulic brake fluid used in the brake system of an automobile, truck, recreational or other vehicle which flushes the hydraulic system of contaminants such as air, water and particulates. Significantly, the present system and method can be carried out as a substantially closed system.
B. Background
Modern motor vehicles have internally-expanding, hydraulically operated brakes. Hydraulic actuation is based on the principle that a pressure exerted upon a liquid is transmitted uniformly in all directions. The typical vehicle brake system comprises a main or master cylinder with a reserve fluid tank, wheel cylinders and connecting brake lines or pipes. Application of the brakes, by depressing the brake pedal, causes a piston in the master cylinder to move and displace hydraulic brake fluid stored in the master cylinder to cause the brake fluid to move through the brake lines. The displaced brake fluid transmits pressure through the fluid filled brake lines to the wheel cylinders that actuate the brake shoe or pad. As a result, the brake shoes or pads are thrust against a brake drum to stop the vehicle's wheels. A pump can be used to increase braking capacity.
Brakes pads, shoes or discs apply a force to particular components, such as the brake drums or rotors that rotate with the wheels. As much as 2,000 pounds psi of hydraulic pressure may be exerted by the brakes on each of the four wheels to stop the vehicle. Brake fluid also acts as a lubricant for the pistons, cylinders, seals and valves that make up the brake system. Different brake systems use different types of brake fluid. All of the brake fluids have certain desirable characteristics and negative aspects. Desirable brake fluid characteristics of brake fluids include high boiling temperature, low freezing temperature and low tendency to bubble. The purity of the brake fluid is important, because if it becomes contaminated the piston seals, hoses and other parts of the brake system may be damaged and have to be replaced. A negative aspect of brake fluid is that it is corrosive to paint and its spillage can harm a vehicle's exterior finish. In addition, inhalation of brake fluid fumes presents a health hazard and spillage of brake fluid presents potential environmental concerns.
Common vehicular brake fluids have ratings such as DOT (Department of Transportation) 3, 4 or 5. DOT 3 brake fluid is recommend for normal city driving, DOT 4 for mountain, trailer towing or frequent hard braking use and silicone based DOT 5 brake fluid for performance or racing vehicles. The higher the DOT rating the higher the boiling point of the brake fluid. However, the higher the boiling point of the brake fluid, the more hygroscopic or water absorbing the brake fluid tends to be. As water is absorbed by the brake fluid its boiling point becomes lower. For instance, a brake fluid having a 3% water content can have a boiling temperature that is 25% lower than a water-free brake fluid. Additionally, at low temperatures the water absorbed by the brake fluid can form ice crystals, which impede free flow of the brake fluid. Thus, the presence of water in the brake fluid can cause a lower boiling point and ice to form, both of which can impair brake function. Even without the problems caused by extreme temperatures, water absorbed by the brake fluid can cause brake components to prematurely rust and fail. Generally, automotive brake fluid should be replaced and the brake system flushed of contaminants when the water level in the brakes fluid is about 3% by volume.
Most brake fluids are clear, volatile, water soluble liquids comprised of a mixture of several alcohols such as glycols. Silicone based (DOT 5) brake fluids are also known. Through use brake fluid can become discolored due to contamination from dirt and disintegrating rubber seals. Additionally, oxygen in the air can oxidize the brake fluid which also reduces its boiling point. Due to its volatile nature and easily absorbed constituents, inhalation of and/or contact with brake fluid can be hazardous.
A lower brake fluid boiling point can result in the brake fluid boiling during a long downhill stretch of intermittent braking. If the brake fluid boils the resulting bubbles reduce brake effectiveness and causes brake fade ("soft brakes") due to the gas bubbles absorbing foot pressure instead of transmitting it through the brake fluid. Particulate matter, such as airborne dust and rubber seal fragments, can also collect within the fluid filled brake lines and reduce braking effectiveness.
To remove water and contaminants, the brake fluid is periodically replaced with new brake fluid. The drained brake fluid is not reused because once exposed to the atmosphere, even if only for a brief period, significant amounts of water, air (with the oxidizing oxygen) and contaminants such as dust can be absorbed by the brake fluid. Even new brake fluid exposed to ambient air can absorb moisture resulting in an immediate loss of the brake fluid's effectiveness. Brake fluid can be tested to determine its viability, such as determining its water content by the method and apparatus disclosed by U.S. Pat. No. 5,028,144. The '144 patent, however, does not disclose an apparatus for removing or replacing spent brake fluid.
As described above, hydraulic brake fluid is periodically replaced due to fluid deterioration and contamination. Many brake fluids have volatile and/or toxic components which can hinder removal and replacement of the fluid. Typically, the entire hydraulic fluid is drained from the brake system and replaced with new fluid, the process being carried out in an open air environment whereby the fluid is exposed to the atmosphere as the brake system is being drained and new fluid is added. Unfortunately, this method releases pollutants into the air and exposes the operator to harmful fluids and vapors. Additionally, no attempt is made to recycle or reuse any of the hydraulic fluid resulting in economic waste and fluid disposal problems. In fact, some states have imposed a fee for the collection and disposal of used brake fluid from automotive service centers, which is typically collected into open containers.
Whether it is necessary to remove and replace the brake fluid is typically determined solely by examining the color of the brake fluid or by automatic replacement after a predetermined period (i.e., after 18 to 24 months or after every 30,000 miles of vehicle usage). If desired, a brake fluid water content test can be done quickly utilizing currently available technology. For instance, brake fluid test strips available from Wagner can be inserted into a vehicle's brake fluid to determine both the type of brake fluid being used and its relative water content. The test is performed much like a pH test in that the a test strip is inserted into the hydraulic fluid and visually reviewed to determine the type of brake fluid and whether the water content is too high. The test method uses samples taken from either the master cylinder or a brake cylinder. The above-described brake fluid test can be run quickly, typically taking less than 1 minute.
The prior art method of replacing brake fluid takes two people about 45 minutes to an hour to remove and replace the brake fluid. The prior art method also requires additional time to clean-up the resulting spillage that is essentially inherent in the prior art method. One commonly known method for removing and replacing a vehicle's hydraulic brake fluid and then removing air introduced into the brake lines by this two person, open system method is shown in FIGS. 1 and 2. Typically, about twice the volume of fluid the caliper can hold per wheel is used by the prior art method. Unfortunately, new brake fluid can become contaminated with moisture, air and particulates as soon as the brake fluid container is opened and poured into the brake system due to the typical open system method used to flush and replace used brake fluid.
What is needed therefore is an apparatus and method for safely removing and replacing hydraulic fluid without exposing the environment or the operator to the brake fluid. Also needed is an apparatus and method for flushing a hydraulic system of contaminants such as air, water and particulates and for safely storing and using new brake fluid while minimizing problems with the removal and disposal of waste brake fluid.